1. Field of the Invention
The present invention relates to a connecting substrate, a connecting structure, a connection method, and an electronic apparatus.
Priority is claimed on Japanese Patent Application No. 2004-228995, filed Aug. 5, 2004, and Japanese Patent Application No. 2005-157057, filed May 30, 2005 the contents of which are incorporated herein by reference.
2. Description of Related Art
Conventionally, when connecting a flexible substrate to a liquid crystal panel, a method is employed in which signals from a drive IC or the like that is mounted on the flexible substrate are transmitted to the liquid crystal panel side by electrically connecting wiring that is formed on the flexible substrate to electrode terminals that are formed at positions on the liquid crystal panel that correspond to the wiring on the flexible substrate.
In recent years, there has been a tendency for the operating frequencies of electronic apparatuses such as liquid crystal display devices and the like to be moved to higher frequencies due to increasing volumes of information, improvements in processing speed, and the like, and there is an increasing demand to transmit a large volume of signals at high speed. In such a situation, in the above-described method to connect wires formed on a flexible substrate to electrode terminals formed on a liquid crystal panel, mismatching in the characteristic impedance from inductor components or the like is generated in the wires on the flexible substrate by this movement of transmitted signals to higher frequencies. As a result, a problem has arisen in that the transmitted signals are degraded.
Therefore, as techniques for this type of high frequency signal transmission, microstriplines and striplines are widely used. Microstriplines are obtained, for example, by forming signal lines on an active surface of a circuit substrate, and by forming solidly formed ground wires to face the signal lines via an insulating layer. Microstriplines are structured such that they can be set to have the desired impedance characteristics. Moreover, striplines are structured, for example, by forming signal lines in an internal layer of the circuit substrate, and by sandwiching the signal lines between solidly formed ground wires. Striplines are also structured such that they can be set to have the desired impedance characteristics.
An example of this type of connecting structure that uses striplines is the structure disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. H06-325836 in which a cut portion is provided by exposing a signal line at a terminal portion of a stripline, and this exposed signal line is then placed in contact with the desired substrate, so as to thereby connect the stripline to the substrate.
However, in the connecting structure disclosed in Unexamined Patent Application, First Publication No. H06-325836, the signal lines that constitute the striplines are connected to the active surface of the substrate being connected, and the ground wires are connected to the rear surface of the substrate being connected. As a result, in the connecting process, it is necessary to handle the two surfaces of the substrate in order to connect the striplines. Furthermore, when connecting the striplines to the substrate, these connections must be made after the positions of each of the stripline signal lines and the electrode terminals formed on the surface of the substrate have been matched, and after the positions of each of the ground wires and the electrode terminals formed on the rear surface of the substrate have been matched. In this manner, in the connecting structure disclosed in Unexamined Patent Application, First Publication No. H06-325836, a problem arises in that the connecting process is made more complex. In addition, in a connecting structure such as that described in Unexamined Patent Application, First Publication No. H06-325836, no consideration is given to cases in which signal lines that are formed in different internal layers of a substrate or on a front or rear of a substrate, such as microstriplines or striplines, are connected to solidly formed ground wires. Consequently, if the signal speed is increased even more in the future, it is probable that the inductor component of the wires will cause problems.